Renal Physiology Practice Questions

Q: A hypertensive patient is found to have a partial obstruction of the renal artery due to an atherosclerotic plaque. The resultant decrease in blood flow causes increased release of an enzyme from which of the following structures?

Juxtaglomerular cells. **Explanation:** The correct answer is **C. Juxtaglomerular cells.** **Mechanism:** This scenario describes **Renovascular Hypertension**. A partial obstruction of the renal artery (e.g., due to atherosclerosis) leads to a decrease in renal perfusion pressure. This drop in pressure is sensed by the **intrarenal baroreceptors** located in the **Juxtaglomerular (JG) cells**, which are specialized modified smooth muscle cells found primarily in the walls of the **afferent arterioles**. In response to decreased stretch (hypotension) or sympathetic stimulation, these cells secrete the enzyme **Renin**. Renin initiates the Renin-Angiotensin-Aldosterone System (RAAS), leading to systemic vasoconstriction and sodium retention to restore blood pressure. **Analysis of Incorrect Options:** * **A. Afferent arterioles:** While JG cells are located *within* the walls of the afferent arterioles, the specific structure responsible for enzyme (Renin) secretion is the JG cell itself. In NEET-PG, always choose the most specific anatomical structure provided. * **B. Arcuate arteries:** These are conduit vessels located at the corticomedullary junction. They do not possess specialized secretory functions for blood pressure regulation. * **D. Kupffer cells:** These are specialized macrophages located in the **liver** sinusoids. They are part of the reticuloendothelial system and are not involved in the RAAS. **High-Yield Clinical Pearls for NEET-PG:** * **Goldblatt Kidney:** This clinical scenario is the human equivalent of the "one-kidney, one-clip" Goldblatt model of hypertension. * **Stimuli for Renin Release:** 1) Decreased perfusion pressure (baroreceptors), 2) Decreased NaCl delivery to the Macula Densa, and 3) Sympathetic stimulation (Beta-1 receptors). * **Histology:** JG cells contain prorenin granules and are considered the "endocrine" component of the Juxtaglomerular Apparatus (JGA).

Q: Which aquaporin channel is primarily mediated through ADH action?

Aquaporin 2. **Explanation:** The correct answer is **Aquaporin 2 (AQP2)**. **Why Aquaporin 2 is correct:** Antidiuretic Hormone (ADH), also known as Vasopressin, regulates water reabsorption in the **Principal cells** of the late distal tubule and collecting ducts. When ADH binds to the **V2 receptors** on the basolateral membrane, it triggers a cAMP-mediated signaling pathway. This causes the translocation of intracellular vesicles containing **Aquaporin 2** channels to the **apical (luminal) membrane**. This increases the water permeability of the membrane, allowing water to be reabsorbed into the hypertonic medullary interstitium. **Why other options are incorrect:** * **GLUT:** These are glucose transporters (e.g., GLUT2 in the proximal tubule) and are not involved in water transport. * **Aquaporin 1:** These channels are constitutively active (always open) and are primarily located in the **Proximal Convoluted Tubule (PCT)** and the descending limb of the Loop of Henle. They are **not** regulated by ADH. * **Aquaporin 3 & 4:** These channels are located on the **basolateral membrane** of the collecting duct cells. While they facilitate the exit of water from the cell into the blood, they are constitutively expressed and not the primary site of ADH-mediated regulation. **High-Yield Clinical Pearls for NEET-PG:** * **Diabetes Insipidus (DI):** Central DI is caused by a deficiency of ADH, while Nephrogenic DI is often due to a defect in the V2 receptor or the **AQP2 channel** itself. * **V2 Receptor:** G-protein coupled receptor (Gs) $\rightarrow$ Adenylyl cyclase $\rightarrow$ cAMP $\rightarrow$ Protein Kinase A $\rightarrow$ AQP2 insertion. * **Lithium:** A common cause of drug-induced nephrogenic DI as it inhibits the signaling pathway that leads to AQP2 expression.

Q: All of the following are true about juxtamedullary nephrons except?

It has a slow rate of filtration.. **Explanation:** In the human kidney, there are two types of nephrons: **Cortical nephrons** (85%) and **Juxtamedullary (JM) nephrons** (15%). **Why Option C is the correct (False) statement:** Juxtamedullary nephrons actually have a **higher Glomerular Filtration Rate (GFR)** compared to cortical nephrons. This is due to their larger glomeruli and higher hydrostatic pressure within the glomerular capillaries. Therefore, stating they have a "slow rate of filtration" is physiologically incorrect. **Analysis of other options:** * **Option A:** It is a standard anatomical fact that JM nephrons constitute approximately **15%** of the total nephron population. * **Option B:** JM nephrons are characterized by **long loops of Henle** that extend deep into the renal medulla, reaching the tips of the renal papillae. * **Option D:** Their primary physiological role is the **concentration of urine**. The long loops of Henle, along with the associated **Vasa Recta** (specialized peritubular capillaries), are essential for maintaining the medullary osmotic gradient via the **counter-current mechanism**. **High-Yield Clinical Pearls for NEET-PG:** * **Vasa Recta:** These are only found associated with Juxtamedullary nephrons; cortical nephrons lack them. * **Renin Content:** Juxtamedullary nephrons contain **less renin** than cortical nephrons. * **Function during Stress:** During periods of decreased renal blood flow (like heart failure), blood is shunted from cortical to JM nephrons to maximize water reabsorption.

Q: Insulin clearance closely resembles:

Glomerular filtration rate (GFR). **Explanation:** The gold standard for measuring the **Glomerular Filtration Rate (GFR)** is the clearance of a substance that is freely filtered by the glomeruli but is neither reabsorbed nor secreted by the renal tubules. **Inulin**, a plant-derived polysaccharide (fructose polymer), perfectly meets these criteria. Since every molecule of inulin filtered at the glomerulus ends up in the urine, its clearance rate is exactly equal to the GFR. **Analysis of Options:** * **A. Glomerular Filtration Rate (GFR):** Correct. Inulin clearance is the reference standard for GFR because its excretion rate equals its filtration rate. * **B. Renal Plasma Flow (RPF):** Incorrect. RPF is measured using substances that are both filtered and completely secreted (like PAH), not just filtered. * **C. Creatinine Clearance:** Incorrect. While used clinically to estimate GFR, creatinine is slightly secreted by the tubules. Therefore, creatinine clearance **overestimates** the true GFR by about 10-20%. * **D. Para-aminohippuric acid (PAH) clearance:** Incorrect. PAH is filtered and almost entirely secreted by the tubules in a single pass. Thus, PAH clearance is used to measure **Effective Renal Plasma Flow (ERPF)**, not GFR. **High-Yield Clinical Pearls for NEET-PG:** * **Criteria for GFR marker:** Freely filtered, not reabsorbed, not secreted, not metabolized, and non-toxic. * **Inulin vs. Creatinine:** Inulin is the most accurate (Gold Standard), but Creatinine is used clinically because it is endogenous (no infusion required). * **Filtration Fraction (FF):** Calculated as GFR / RPF. Normal value is approximately 0.20 (20%). * **Clearance Ratio:** If Clearance of X / Clearance of Inulin 1, the substance is being secreted (e.g., Penicillin).

Q: Which of the following is NOT an endocrine function of the kidney?

Natriuretic peptide secretion. The kidney is a vital organ with both excretory and non-excretory (endocrine) functions. This question tests the ability to distinguish between hormones produced by the kidney versus those that act upon it. ### **Why Option B is Correct** **Natriuretic peptides** (specifically ANP and BNP) are primarily secreted by the **heart** (atria and ventricles, respectively) in response to increased wall stretch or volume overload. While these peptides act on the kidney to promote sodium excretion (natriuresis) and water loss, they are **not produced by the kidney**. ### **Why Other Options are Incorrect** * **Option A (Erythropoietin):** Produced by **interstitial cells in the peritubular capillary bed** of the renal cortex. It stimulates RBC production in the bone marrow in response to hypoxia. * **Option C (1,25-dihydroxyvitamin D3):** The kidney contains the enzyme **1-alpha-hydroxylase** (in the PCT), which converts inactive 25-hydroxyvitamin D into the active form, **Calcitriol**. * **Option D (Renin):** Secreted by the **Juxtaglomerular (JG) cells** of the afferent arteriole. It is the rate-limiting step of the Renin-Angiotensin-Aldosterone System (RAAS). ### **NEET-PG High-Yield Pearls** * **Prostaglandins (PGE2, PGI2):** Also produced by the kidney; they maintain renal blood flow by vasodilating the afferent arteriole. * **Thrombopoietin:** While primarily produced in the liver, a small amount is synthesized in the kidney. * **Chronic Kidney Disease (CKD) Correlation:** Patients with CKD often present with **anemia** (due to EPO deficiency) and **renal osteodystrophy** (due to Vitamin D activation failure).

Q: In which of the following conditions is renin secretion inhibited?

Hypervolemia. **Explanation:** Renin is an enzyme secreted by the **Juxtaglomerular (JG) cells** of the afferent arteriole in response to perceived low blood pressure or low sodium delivery. Its primary role is to initiate the Renin-Angiotensin-Aldosterone System (RAAS) to restore blood volume and pressure. **Why Hypervolemia is Correct:** **Hypervolemia** (increased extracellular fluid volume) leads to increased renal perfusion pressure and increased stretch of the afferent arteriole. This inhibits the release of renin. Additionally, hypervolemia often leads to the release of **Atrial Natriuretic Peptide (ANP)** from the heart, which directly inhibits renin secretion to promote sodium and water excretion. **Analysis of Incorrect Options:** * **Cirrhosis:** In advanced cirrhosis, peripheral vasodilation (splanchnic pooling) leads to "effective" arterial underfilling. This triggers the baroreceptors to **increase** renin secretion to maintain blood pressure. * **Exercise:** Exercise activates the **Sympathetic Nervous System**. Sympathetic stimulation of β1-receptors on JG cells is a potent trigger for **increasing** renin release. * **Cardiac Failure:** In heart failure, the reduced cardiac output results in decreased renal perfusion. The body perceives this as hypovolemia, leading to a compensatory **increase** in renin secretion (secondary hyperaldosteronism). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulants of Renin:** Decreased BP, decreased NaCl delivery to Macula Densa (via NKCC2), and Sympathetic stimulation (β1). * **Inhibitors of Renin:** Increased BP, Angiotensin II (negative feedback), ANP, and Hyperkalemia (direct effect). * **Goldblatt Kidney:** A classic experimental model where renal artery stenosis leads to high renin hypertension. * **Bartter Syndrome:** Characterized by hyperplasia of JG cells leading to hyperreninemia.

Question 1

What is the effect of sympathetic stimulation on Glomerular Filtration Rate (GFR)?

Accepted Answer

Decreased GFR with afferent arteriolar constriction

Answer

Increased GFR with afferent arteriolar dilatation

Answer

Increased GFR with efferent arteriolar constriction

Answer

Decreased GFR with efferent arteriolar dilatation

Question 2

A hypertensive patient is found to have a partial obstruction of the renal artery due to an atherosclerotic plaque. The resultant decrease in blood flow causes increased release of an enzyme from which of the following structures?

Accepted Answer

Juxtaglomerular cells

Answer

Afferent arterioles

Answer

Arcuate arteries

Answer

Kupffer cells

Question 3

Which aquaporin channel is primarily mediated through ADH action?

Accepted Answer

Aquaporin 2

Answer

GLUT

Answer

Aquaporin 1

Answer

Aquaporin 3

Question 4

Atrial Natriuretic Peptide (ANP) causes what change?

Accepted Answer

Increase in blood volume

Answer

Increase in cardiac output

Answer

Increase in urine output

Answer

Decrease in renin secretion

Question 5

All of the following are true about juxtamedullary nephrons except?

Accepted Answer

It has a slow rate of filtration.

Answer

It forms 15% of total nephrons.

Answer

It has a long loop of Henle.

Answer

Major function is concentration of urine by counter-current mechanism.

Question 6

Insulin clearance closely resembles:

Accepted Answer

Glomerular filtration rate (GFR)

Answer

Renal plasma flow

Answer

Creatinine clearance

Answer

Para-aminohippuric acid (PAH) clearance

Question 7

Which of the following is NOT an endocrine function of the kidney?

Accepted Answer

Natriuretic peptide secretion

Answer

Erythropoietin secretion

Answer

1,25-dihydroxyvitamin D3 formation

Answer

Renin secretion

Question 8

Arrange the following in increasing order of their contribution to total renal vascular resistance: Afferent arteriole, Renal artery, Interlobar, arcuate and interlobular arteries, Peritubular capillaries?

Accepted Answer

Renal artery - Interlobar, arcuate and interlobular arteries - Peritubular capillaries - Afferent arteriole

Answer

Afferent arteriole - Interlobar, arcuate and interlobular arteries - Peritubular capillaries - Renal artery

Answer

Peritubular capillaries - Afferent arteriole - Interlobar, arcuate and interlobular arteries - Renal artery

Answer

Interlobar, arcuate and interlobular arteries - Peritubular capillaries - Afferent arteriole - Renal artery

Question 9

In which of the following conditions is renin secretion inhibited?

Accepted Answer

Hypervolemia

Answer

Cirrhosis

Answer

Exercise

Answer

Cardiac failure

Question 10

Over half of the potassium that appears in the urine of a patient, who has ingested some potassium salts, is derived from which source?

Accepted Answer

Secretion by the distal tubule

Answer

Glomerular filtrate

Answer

Reabsorption in the proximal tubule

Answer

Secretion by the loop of Henle

Renal Physiology — MCQs

Renal Physiology — MCQs

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